Yeah, it's been a crazy week workwise, and it's not looking like it'll be getting any saner anytime soon. But I will publish the next chapter from the book soon. SOON.
As for how the card works - I have a BTC balance on Xapo. The card is in USD (and works pretty much anywhere Visa works). So the payment in USD comes off the balance in BTC. They probably take some cut, and the card itself cost about $20 to order and get. Still worth it.